The clamping device for workpieces forged in forging manipulators are formed with two gripper arms, or four gripper arms which are pivotable in pairs in intersecting planes, in a bearing head, which arms at one of their ends support clamping jaws pivotable about axes parallel to the pivot axes of the respective gripper arms. At their other ends, displacement means, such as piston-cylinder units which act directly or by way of wedges, links or push rods, act upon the gripper arms by which means the closure of the grippers is effected. In general there are only two gripper arms, which are provided with clamping jaws with V-shaped grooves. The invention relates to clamping devices which are provided with four gripper arms and four clamping jaws.
The clamping devices provided with four gripper arms with clamping jaws generally comprise, like the clamping devices provided with only two gripper arms with clamping jaws, only a single displacement means, by which the gripper arms with their clamping jaws are moved uniformly and in the same direction. As a result these clamping devices are suitable only for clamping workpieces whose clamping areas are at the same distance, in the planes intersecting at right angles, from the axis of the workpiece in the clamping area, for example a circular or square cross-section. For clamping forged pieces with a non-round cross-section in the clamping area, for example a rectangular or oval cross-section, it is known (German Patent DE No. 24 11 112) to construct the gripper arms which can be moved in pairs independently of one another, each pair of grippers having associated with it its own displacement means comprising a piston with a head member connected by way of push rods to the gripper arms of the pair, and the displacement means pistons being a solid piston and an annular piston arranged coaxially in a common cylinder connected to the bearing head of the gripper arms and mounted rotatably in the frame supporting the clamping device.
The solid and annular pistons, provided for the independent separate movement of the gripper arms in pairs in accordance DE No. 24 11 112, do not permit the delivery of tools or of workpieces from the rear or their removal through the clamping device, as is desired, however, in particular in forging manipulators which cooperate with so-called forging machines, whose rams and tools arranged in an X-shaped are moved radially to the workpiece. In this connexion the space required for the two nested pistons is a disadvantage. The object of the invention is to overcome the aforesaid disadvantages by a support, space-saving design of the clamping device.